A storage area network (SAN) may be implemented as a high-speed, special purpose network that interconnects different kinds of data storage devices with associated data servers on behalf of a large network of users. Typically, a storage area network includes high performance switches as part of the overall network of computing resources for an enterprise. The storage area network is usually clustered in close geographical proximity to other computing resources, such as mainframe computers, but may also extend to remote locations for backup and archival storage using wide area network carrier technologies. Fibre Channel networking is typically used in SANs although other communications technologies may also be employed, including Ethernet and IP-based storage networking standards (e.g., iSCSI, FCIP (Fibre Channel over IP), etc.).
As used herein, the term “Fibre Channel” refers to the Fibre Channel (FC) family of standards (developed by the American National Standards Institute (ANSI)) and other related and draft standards. In general, Fibre Channel defines a transmission medium based on a high speed communications interface for the transfer of large amounts of data via connections between varieties of hardware devices.
FC standards have defined limited allowable distances between FC switch elements. Fibre Channel over IP (FCIP) refers to mechanisms that allow the interconnection of islands of FC SANs over IP-based (internet protocol-based) networks to form a unified SAN in a single FC fabric, thereby extending the allowable distances between FC switch elements to those allowable over an IP network. For example, FCIP relies on IP-based network services to provide the connectivity between the SAN islands over local area networks (LANs), metropolitan area networks (MANs), and wide area networks (WANs). Accordingly, using FCIP, a single FC fabric can connect physically remote FC sites allowing remote disk access, tape backup, and live mirroring.
In an FCIP implementation, FC traffic is carried over an IP network through a logical FCIP tunnel. Each FCIP entity on either side of the IP network works at the session layer of the OS model. The FC frames from the FC SANs are encapsulated in IP packets and transmission control protocol (TCP) segments and transported in accordance with the TCP layer in a single TCP session. For example, an FCIP tunnel is created over the IP network and a TCP session is opened in the FCIP tunnel. All traffic is then communicated through the FCIP tunnel in the same TCP session.
Different priorities may be assigned to different FC data streams to provide different levels of quality of service (QoS). For example, a video data stream may be given a higher priority than a tape backup data stream, which is not as sensitive to performance problems or to the inherent delays in reordering packets that have arrived out-of-order. However, by passing FCIP traffic through a single TCP session, all levels of service are similarly affected during IP network congestion. As such, all FCIP traffic in the FCIP tunnel is effectively treated with the same level of priority. In this implementation, FC data streams having different levels of priority (e.g., different qualities of service or QoS levels) may lose their distinct priorities while in the IP network.